Optical fibers and optical fiber cables have become the preferred telecommunications transmission medium used in the United States and in the world. Fiber optic cables have revolutionized the long distance telecommunications industry and are also penetrating into local telephone markets and CATV (cable television) markets, displacing older technologies. Optical transmission offers numerous advantages over prior technology. For example, a fiber optic cable may provide a transmission distance of fifty miles or more with currently available electronics, may transport digital light pulses for essentially noise free communications and transmissions of vast quantities of information. The fibers, when used to transmit information in a digital signal form, are useful over wide signal bandwidths, and can replace both coaxial cables currently used for broadband signals and copper pair cables currently used for narrowband voice signals. Fiber optic cables are thus taking the place of conventional cables due to their high bit rate capacity, small size, and light weight. However, most home and office electronic devices are not adapted to receive optical signals. Thus, in general, the optical signal must be converted to an electrical signal before it is supplied to the end user.
In many cases, fiber optic cable is supplied to an optical network unit (ONU). At that point, the optical signal is converted into an electrical signal, after which it is transmitted to the end user. If the electrical signal is being provided to a multi-story, multi-user building, the ONU may be located in, for example, the basement of the building. Otherwise, the ONU may be located at a central, off site, location from which multiple lines are run to multiple users.
The conversion of an optical signal to an electrical signal requires electricity, which is most commonly obtained from tapping off the neighborhood or household electrical power lines. However, this has a disadvantage in that localized power outages will also cause disruption of the electrical communications signal. In addition, the cost of converting the optical signal to an electrical signal cannot be adequately charged to each end user due to fluctuations in usage rates.
One solution to the above problem is disclosed in U.S. Pat. No. 5,268,971 issued to Nilsson et al. This patent discloses a composite cable having a bundle of optical fibers and a plurality of insulated metallic conductors all wrapped within an aluminum shield. The shield is covered by steel armor. This cable is inadequate for the purposes described above because it is extremely awkward to handle. The aluminum shield and steel armor render the cable unmanageable and the power conductors and optical fibers are inaccessible to a worker making splices and/or working on the cable.
Another composite cable is disclosed in U.S. Pat. No. 4,375,313 issued to Anderson et al. The cable disclosed therein has a central cushioning core about which are helically wrapped one or more optical fibers. A further cushioning blanket is wrapped about the optical fibers. The blanket is wrapped by a tape jacket preferably formed of metal. A plurality of strength members form a jacket about the optical fiber core and one or more electrical conductors can be located between the jacket and the core. A disadvantage of this cable is the requirement of wrapping and unwrapping the metallic jacket in order to gain access to the transmission media.
Another composite cable having both optical fibers and electrical conductors is taught by Barrett et al. in U.S. Pat. No. 5,189,718. In this cable, the electrical conductors are contained in one tube and the optical fibers are contained in a second tube. The first and second tubes are connected by a web. This cable has the disadvantage that splicing both cables in one closure is awkward and difficult.
Apparently, the prior art is devoid of a cable which provides both metallic and optical fiber conductors in a simple, easy to splice arrangement. The ideal cable should have sufficient strength to function as a distribution cable, but should not be too heavy or unmanageable for use within a building. In addition, the deal cable should be easily manipulatable by a worker so that he or she can easily cut the cable and splice the electrical conductors and optical fibers as needed. The ideal (able should have appropriate waterblocking features to prevent the ingress of water and should have appropriate strength features to protect the optical fibers.